Improvement of the heat resistance of rubber material has been so far made by addition of an antioxidant thereto. Heat resistance and aging resistance can be very effectively improved by the addition of the antioxidant, but further improvement of heat resistance is still now a requirement for prolonging the product life.
However, it is the accepted knowledge that there is an optimal amount of the antioxidant to be added, and even a simple increase in the amount of antioxidant to be added can never contribute to a desired functional improvement, corresponding to such an increment of the added antioxidant. Addition of a larger amount of the antioxidant than the optimal amount will inhibit the cross-linking reaction and also will lower the physical properties of the resulting rubber material. From the viewpoint of productivity, high speed cross-linking of rubber is required, and cross-linking retardation (cross-linking inhibition) has an adverse effect on product cost. Thus, it has been desired to attain high speed cross-linking and also to improve the product life, without addition of a large amount of an antioxidant to a rubber layer.
Rubber materials are often used upon compositing with metallic materials, where, for example, an aqueous latex of rubber is applied to a metallic sheet, followed by cross-linking to conduct compositing. In that case, an antioxidant must be added to an aqueous latex of rubber to make the resulting rubber layer contain the antioxidant, but by the initial addition of the antioxidant the latex will, in some cases, loose the dispersion stability, resulting in gellation and molding failure of rubber materials, whereas without the addition of the antioxidant no improvement of the heat resistance of the rubber materials can be attained. This is a problem.
Generally, the rubber materials have some tackiness due to a flexibility in the nature, so extraneous matters such as dusts, etc. are liable to attach to the tacky surface, creating disagreeable touch and mutual adhesion of rubber products themselves, and thus surface coating with an antitack agent is often carried out to improve the surface tackiness. However, such a surface tack prevention treatment leads to increasing cost of rubber products, so their application and use are often restricted.